1. Field of the Invention
This invention relates to balanced digital time displays which are useful for general purpose timekeeping, i.e., the timekeeping needs and practices of ordinary individuals engaged in their usual day-to-day activities.
2. Description of the Prior Art
Balanced digital time displays are described in U.S. Pat. Nos. 4,264,966, 4,271,497, 4,483,628 and 4,627,737, the disclosures of which are incorporated herein by reference. Typically these patents teach the display of both elapsed time and remaining time during the course of each hour. This is accomplished by displaying, at the beginning of an hour, centrally located current hour digits followed by incrementing elapsed minutes to the right of the hour digits and, optionally, seconds below the hour digits cycling either from zero to thirty to zero, or from zero to fifty nine, during each elapsed minute.
Approximately halfway through the hour the display switches to show remaining time, by advancing the value of the centrally located hour digit to the next hour, and by transposing and decrementing the minute digits to the left of the next hour digit, with seconds cycling either from zero to thirty to zero, or from fifty nine to zero, during each remaining minute. In effect, these displays reference time back to the onset of the current hour during the first half hour, and then reference forward the remaining time during the second half hour to the approach of the next hour, thereby providing a dual digital perspective and quantification of the intervals between the current exact time and the beginning and ending of each hour.
Such balanced digital time displays have an inherent characteristic which has caused problems when the displays are sought to be set or reset in the remaining time mode. In that mode, the display typically shows the value of each forthcoming minute and the number of seconds remaining to that minute, e.g., the twenty fifth minute and fifty nine seconds, before the next hour. That twenty fifth minute remains displayed during the interval that seconds decrement from fifty nine to zero, at the end of which the exact time shown is twenty five minutes and zero seconds before the next hour. At the very next second, the minute value automatically steps down to twenty four, and seconds resume decrementing from fifty nine to zero to count down the interval remaining to that next minute.
Thus, in the remaining time mode, the value of each exact minute and zero seconds before the next hour is seen for only one second, because the display thereafter decrements to the next remaining minute for the next fifty nine seconds, and so on. As a result, if the display is reset to an exact time announcement while showing remaining time, the value of the minute at that exact time will be seen for only the fleeting interval of one second before the minute value automatically decreases by one unit to the value of the next remaining minute, an effect which some viewers have perceived as odd or disconcerting.
Just the opposite occurs during the elapsed time mode. In that mode, as the value of each exact minute and zero seconds is reached and displayed, the minute value remains on view for the next fifty nine seconds before the display increments to the next minute. For example, if the exact time is ten minutes past the hour, the viewer will initially see ten minutes and zero seconds and will continue to see the tenth minute displayed for the next fifty nine seconds. At the next second, the value of the eleventh elapsed minute will appear with zero seconds and will remain displayed for the next fifty nine seconds, and so on.
Thus, a specific comparison of the two modes will illustrate their opposite and seemingly anomalous characteristics when exact minutes occur. Consider, for example, the exact time of six thirty four, i.e., thirty four elapsed minutes and zero seconds after the sixth hour which, in its remaining time equivalent, is twenty six minutes and zero seconds before the seventh hour. One second before this exact time, the elapsed time display would show thirty three minutes and fifty nine seconds past the sixth hour, and the equivalent remaining time display would show twenty six minutes and one second before the seventh hour. At the next second, the elapsed time display would increment to exactly thirty four minutes and zero seconds past the sixth hour, but the equivalent remaining minute value would not change--it would stay at twenty six minutes with zero seconds before the seventh hour. Only after the next second would the remaining time display decrement to twenty five minutes and fifty nine seconds before the seventh hour, while the equivalent elapsed time display would remain steady at thirty four minutes plus one second.
Accordingly, balanced digital time displays present what appears to be a lack of synchronism between the elapsed and remaining time modes because in the one second interval that elapsed minutes increment to the next higher value, there is no change in the equivalent remaining minute, whereas after the next second, while the elapsed minute value remains the same, the equivalent remaining minute decrements to the next lower value. This apparent one second mismatch between the elapsed and remaining time modes exacerbates the previously discussed difficulties arising from the fact that setting to an exact elapsed minute retains the resulting minute value for the next fifty nine seconds, but setting to an equivalent exact remaining minute loses the resulting minute value after only one more second, thus accentuating the seemingly asynchronous anomalies between the two modes.
Confronted with these problems, certain workers in the art have resorted to a solution which has left much to be desired. Specifically, in producing prototype wristwatches incorporating the teachings of U.S. Pat. No. 4,627,737, such workers artificially advanced real time by one second at the moment of transition from the elapsed to remaining time modes. In other words, after reaching thirty minutes and twenty nine seconds past the current hour, instead of incrementing the display to thirty minutes and thirty seconds at the next second, the display was programmed to skip over that value and jump ahead to twenty nine minutes and twenty nine seconds before the next hour.
The idea behind this one second advance of real time was to cause both incrementing of elapsed minutes and decrementing of equivalent remaining minutes to occur at the same point in time, thereby eliminating the apparent mismatch and asynchronism between the elapsed and remaining time modes. In fact, this result was achieved, which will be understood by reference again to the previously discussed comparative specific example. By advancing the remaining time display ahead by one second, for example, at thirty three minutes and fifty nine seconds past the sixth hour, the equivalent remaining time display showed twenty six minutes and zero seconds before the seventh hour, instead of the actual real time of twenty six minutes and one second before the seventh hour. After the next second, the elapsed time display incremented to thirty four minutes and zero seconds past the sixth hour, whereas the equivalent remaining time display decremented to twenty five minutes and fifty nine seconds before the seventh hour, instead of the actual real time of twenty six minutes and zero seconds. Thus, the two display modes were caused to undergo simultaneous transitions when stepping up and down from minute to minute during the remaining time period, and the apparently anomalous characteristics and mismatch between the elapsed and remaining time modes during this period were eliminated.
At least two undesirable effects resulted from the above described solution. First, since the display was caused to move ahead by one second from exact real time beginning at the transition from elapsed to remaining time, it thereafter showed time that was correspondingly incorrect by that amount for the balance of the remaining time period. In fact, at the next transition from remaining time to elapsed time, i.e., at the commencement of the next hour, it became necessary to insert a corresponding one second delay of real time to compensate for and eliminate the previous one second advance, thereby restoring the display to the correct time. Thus, in the prototype wristwatches, the time was always incorrect, i.e., too fast by one second, throughout the remaining time mode, an obviously undesirable condition, particularly for a digital form of time display which is expected to show time with exceptional exactness and accuracy.
A second problem was that by maintaining the one second advance of real time throughout the period of the remaining time mode, the display always automatically reset to the next remaining minute and fifty nine seconds whenever it was set to any exact minute time announcement. This came about because the display was always one second too fast and whenever setting was attempted to an exact minute, the true value of each such minute and zero seconds had already been displayed and passed one second earlier. For example, in resetting the display to twenty four minutes before the next hour, at the moment of an announcement of that exact time (in terms of its equivalent thirty six minutes past the current hour), the viewer instead saw twenty three minutes and fifty nine seconds before the next hour. Thus, the viewer could never synchronize the display to correct exact values of specific remaining minutes and zero seconds before the next hour in the remaining time mode, but instead always saw the value of the next remaining minute and fifty nine seconds, whenever the display was reset during the second half hour. This anomaly has been perceived as also, if not more, strange and disconcerting than the difficulties it was designed to solve and has seriously complicated the setting or resetting of balanced digital time displays.